(Meth)acrylamide is a compound useful as a raw material of a (meth)acrylamide-based polymer, and particularly, an acrylamide-based polymer is widely used as a paper strength increasing agent, a coagulant or the like.
In recent years, as a process for producing (meth)acrylamide, a process using a microbial catalyst instead of a copper catalyst has been paid attention because it has advantages such that the reaction conditions are mild and the amounts of by-products are extremely small (see patent document 1). In this process, (meth)acrylonitrile is hydrated by an enzyme contained in the microorganism, i.e., nitrile hydratase, and thereby converted into (meth)acrylamide. Through this process, acrylamide is obtained as an aqueous solution of 40 to 80% by weight, and methacrylamide is obtained as an aqueous solution of 10 to 40% by weight. When the resulting (meth)acrylamide is used as a raw material of a (meth)acrylamide-based polymer, acrylamide is preferably supplied as an aqueous solution of 40 to 60% by weight or a crystalline product, and methacrylamide is preferably supplied as an aqueous solution of 10 to 20% by weight or a crystalline product.
In the case where such a (meth)acrylamide aqueous solution as above is produced using a biocatalyst, and if (meth)acrylamide is introduced in a concentration lower than the concentration in the end product to the subsequent step of performing separation of impurities such as a microbial catalyst, there occurs a problem that the concentration of (meth)acrylamide is further lowered in the subsequent step. Therefore, it becomes necessary to perform a step of adjusting the concentration of (meth)acrylamide to that in the end product, such as a water removal step by distillation or the like, after the above-mentioned subsequent step of performing separation of impurities. Further, there is another problem that such a removal step leads to an increase in production cost.
Also in the case where such a crystalline product of (meth)acrylamide as above is produced, it is necessary to increase a concentration ratio or to decrease a crystallization temperature in order to obtain a difference in concentration required for crystallization, so that there is a problem of an increase in cost.
Patent document 1: Pamphlet of International Publication No. 2003/033716